The major objective of this proposal is to produce monospecific antibiodies to erythropoietin (ESF) in order to further isolate the hormone and to study its interaction with hematopoietic cells. The methods involve the production of antibodies in hybrids formed between a mouse plasmacytoma line and lymphocytes from mice immunized with a human ESF preparation. Once clones have been established producing monospecific antibody, the antibody will be used in the following ways: 1) To be used on affinity columns in order to bind ESF. Antibody and antigen will then be dissociated and studies carried out on the ESF recovered. 2) The antibody will be either labeled with a fluoresceinated dye, radioactive Iodine, or conjugated to ferritin for studies of hormone binding to possible target cells. The establishment of hybrid clones capable of producing monospecific antibody to ESF will enhance knowledge of the hormone's physiology and cell biology by leading to avenues of both target cell and hormone purification.